The translational machinery of the ribosome performs the essential task of protein synthesis. In order to do this it must properly coordinate the interaction of the anticodon of each tRNA with the appropriate mRNA codon and catalyze peptidyl bond formation at a site more than 70 A away. The relatively constant rate of protein synthesis implies that each tRNA must interact with the ribosome similarly, despite significant differences in tRNA sequence, amino acid identity, and anticodon identity. It has been suggested that small differences tRNA structure and the presence of modified residues play a role in modulating the interactions of tRNA with the ribosome. Novel methods of tRNA construction, in concert with new thermodynamic and kinetic assays, will be applied to (1) determine how different tRNAs are built to maintain uniform ground-state thermodynamic interactions with the ribosome, and (2) to establish how tRNA structure modulates the movement of tRNAs on the ribosome during translation. The experiments are designed to understand the dependence of protein synthesis on tRNA-ribosome interactions.